1. Field of the Invention
The present invention relates to an eco-run control device that has an eco-run function to drive a vehicle while starting and stopping the engine, and to an engine restart method.
2. Description of the Related Art
In recent years, to improve fuel efficiency and reduce emission, there have been eco-run control devices mounted on vehicles. An eco-run control device issues an engine stop instruction when predetermined engine stop requirements are satisfied, and later issues an engine restart instruction to drive an engine starting motor when predetermined engine start requirements are satisfied.
An eco-run ECU that performs eco-run control operations determines whether to stop the engine and whether to start the engine, based on an eco-run allowing signal and an eco-run prohibiting signal transmitted from another ECU, and signals transmitted from various sensors and actuators.
FIG. 1 illustrates the structures of an eco-run ECU 100 and an engine ECU 200 that controls the engine. When the vehicle comes to a halt and enters an eco-run control state, the eco-run ECU 100 outputs an eco-run start request to the engine ECU 200. Upon receipt of the eco-run start request, the engine ECU 200 cuts the fuel supply and stops the engine.
When the engine is started, a start request detecting unit 101 of the eco-run ECU 100 detects a starting operation of the driver (a shift operation, a brake operation, a clutch operation, or the like), and transmits an engine start request to the engine ECU 200. Based on information such as the engine speed, a starter drive allowing/prohibiting unit 201 of the engine ECU 200 determines whether the engine needs to be started by a starter motor. If the starter drive allowing/prohibiting unit 201 determines that the engine needs to be started by the starter motor, a starter drive allowing signal is output to the eco-run ECU 100. If the starter drive allowing/prohibiting unit 201 determines that the engine does not need to be started by the starter motor, a starter drive prohibiting signal is output to the eco-run ECU 100. The eco-run ECU 100 has a starter motor driving unit 102. When the starter drive allowing signal is output from the engine ECU 200, the starter motor driving unit 102 drives the starter motor to start the engine.
Japanese Unexamined Patent Publication No. 2006-233917 discloses a monitoring electronic device that monitors an idling stop control electronic device for an error. If there is an error in the idling stop control electronic device, the monitoring electronic device puts the starter motor into a stopped state.
However, if there is failure in the communication circuit in the engine ECU, a disconnection in the communication line, a noise in a communication, or the like, the eco-run ECU cannot receive the starter drive allowing signal or the starter drive prohibiting signal from the engine ECU side. In such a case, the eco-run ECU cannot determine anything, and there is a possibility of engine failure. Japanese Unexamined Patent Publication No. 2006-233917 does not disclose a technique for preventing engine failure.
Also, even if the communication between the engine ECU and the eco-run ECU is in a normal state, engine failure might occur before a response is received from the engine ECU, due to a communication delay.
FIG. 2 shows an example of a communication between the eco-run ECU 100 and the engine ECU 200. When the start request detecting unit 101 of the eco-run ECU 100 detects a starting operation of the user (the timing A in FIG. 2), the information about the detection of the start request is written in a RAM of a communication end that communicates with the engine ECU 200 (the timing B in FIG. 2: 1 ms). The detection result written in the RAM of the communication end is transmitted to the engine ECU 200 by a communication application (the timing C in FIG. 2: 16 ms). When receiving the information from the eco-run ECU 100 (the timing D in FIG. 2: 1 ms), the engine ECU 200, writes the received information in the communication RAM through a register (the timing E in FIG. 2: 1 ms).
The information written in the communication RAM is then written in a RAM to be used by the application on the side of the engine ECU 200 (the timing F in FIG. 2: 8 ms), and is read by the engine ECU 200 to determine whether the engine needs to be started by the starter motor (the timing G in FIG. 2: 16 ms). The determination result is then transmitted from the engine ECU 200 to the eco-run ECU 100. This transmission is performed through the same procedures as those of a communication from the eco-run ECU 100 to the engine ECU 200, and takes the same amount of communication time as a communication from the eco-run ECU 100 to the engine ECU 200 (the timing H in FIG. 2: 43 ms).
Since approximately 100 ms is required at worst between the detection of a starting operation of the driver and the reception of the starter drive allowing/prohibiting signal from the engine ECU 200, there is a possibility that engine failure occurs before a response is received from the engine ECU 200.